1. Field of the Invention
This invention relates to a flash photographing apparatus.
2. Description of the Prior Art
Japanese Laid-Open Patent Application No. SHO 49-53418 discloses a technique for flash photography. According to the disclosure, a flash device is arranged to perform a pre-flashing action on an object to be photographed. A reflection light thus obtained from the object is detected through the lens (TTL) of a camera by means of a light receiving photo-sensitive element which is disposed within the camera. The quantity of the detected reflection light is integrated. Concurrently with this integrating process, a photo-sensitive element disposed close to the flashing part of the flash device directly detects the pre-flash light instead of the reflection light coming from the object. The quantity of the pre-flash light thus detected is also integrated. When the amount of the former integration reaches a predetermined level which varies with the sensitivity of the film in use, the latter integrating process is stopped. The result of the latter is stored. Following this, a main flashing action is performed. The quantity of the main flash light is detected by the photo-sensitive element disposed close by the flashing part. When the detected flash light quantity comes to be in a predetermined ratio to the above-stated result of integration, i.e. when the main flash light quantity reaches a predetermined relation to the pre-flash light quantity, the main flashing action is brought to a stop.
In accordance with the prior art technique disclosed in the above-cited Japanese patent application, the sequence of processes from pre-flashing to photographing including the detection of a reflection light resulting from pre-flashing, storing the level of the reflection light and performing the main flashing immediately after completion of pre-flashing are carried out in an automatic manner without allowing the photographer to know the photographic data obtained by pre-flashing.
However, according to this prior art disclosure, an arrangement to modify the continuous performance of the pre-flashing and the main flashing processes to have a sufficient period of time between these processes in a time serial manner makes it necessary to stop down the aperture of a photo-taking lens at the time of pre-flashing in the same manner as in exposing the film to light. This not only complicates the operation of the camera but also makes correction of an exposure difficult after pre-flashing.
To solve this problem, another technique was disclosed in Japanese Laid-Open Patent Application No. SHO 59-78325. In this case, in performing the pre-flashing process, light measurement is accomplished without stopping down the aperture of the photo-taking lens and the exposure correction is arranged to be carried out by performing a computing operation on information obtained by the pre-flashing and information about an aperture value. The disclosure further included an arrangement to make a bar display showing the quantity of flash light to be obtained by main flashing. This arrangement is called "flash EE lock."
The disclosed arrangement is capable of showing, when the pre-flashing action is performed, a quantity of main flash light required for adequately photographing an object. However, the arrangement is incapable of displaying any information on a measured light value determined on the basis of the result of measuring the exterior light or ambient light (such as a shutter time value or an aperture value determined on the basis of the level of the ambient light). For example, in taking a picture of a person standing with a twilight in the background by synchronized flash photography, it has been difficult to have both the person and the background adequately photographed, because: While the person which is the main object can be adequately photographed on the basis of the data obtained by pre-flashing, the aperture or the shutter time which must be adjusted for adequately photographing the background objects according to the brightness of the ambient light is automatically set for flash photography in response to completion of a charging process on a main capacitor irrespective of the brightness or luminance of these objects. Under that condition, therefore, such objects are not always adequately photographed and tend to be inadequately contrasted with the main object.
Further, in the same prior art arrangement, the information obtained by the pre-flashing and information on the aperture value, etc., required for actual photographing, are computed to obtain a quantity of light to be flashed during the main flashing action. By this, the main flash light quantity can be determined always at a value required for adequately photographing the object independently of any variations in the information about the aperture value, etc. In this case, however, the above-stated determination of the main flash light quantity is made without comparing it with the maximum flash light quantity available from the flash device. The prior art arrangement therefore has been incapable of giving any warning in the event that the main flash light quantity thus determined is in excess of the maximum light quantity available from the flash device.
In the case of flash photography using a flash device in combination with a camera of the kind having a focal plane shutter, if a photographing operation is performed at a shutter speed higher than a flash synchronizing speed, the image plane would not have its whole area exposed to the flash light and thus would come to have a slit exposure. To avoid this, many of known flash photographing apparatuses have been arranged as follows: Upon completion of a charging process on a main capacitor of a flash device with the flash device mounted on a camera, the shutter time of the camera is automatically shifted to a synchronizing shutter time irrespective of the shutter time value set on the camera.
Despite such an arrangement, however, if the charging process on the main capacitor is completed after a shutter time value has been determined with an operation performed on a shutter release button, an X-contact turns on to cause, upon completion of the travel of the leading curtain of the shutter, the flash device to flash. In that event, the photographing operation also results in a slit exposure.
Further, in the majority of the conventional flash photographing systems, flashing is arranged to be performed when the X-contact is turned on after completion of the travel of the leading shutter curtain. Further, as in the case of Japanese Laid-Open Patent Application No. SHO 56-168480, some of such systems are arranged to perform flashing immediately before commencement of the travel of a trailing shutter curtain. None of these prior art systems have been, however, arranged to freely determine a timing for flashing in an appropriate manner. Therefore, there has been known no flash photographing system that is capable of selecting an appropriate timing for flashing while the shutter is in an open state.